The Effect of Genetic Merit for Fertility Traits on Regulation of the Somatotropic Axis in Hepatic Tissue in Holstein cows08 February 2013
An in depth look into the complex science behind genetic traits for fertility is given in this project outline by researchers at Teagasc.
The growth hormone/insulin-like growth factor (somatotropic) axis is seen as an important biological mechanism linking nutritional status and reproduction (Lucy, 2001). We previously reported that genetic merit for fertility traits is associated with significant changes in reproductive efficiency, BCS profile and circulating concentrations of IGF-I (Cummins et al., 2011). Cows with good (Fert+) genetic merit for fertility traits had greater circulating concentrations of IGF-I throughout lactation compared with cows with poor (Fert-) genetic merit for fertility traits. The aim of this study was to determine the effect of genetic merit for fertility traits on transcriptional regulation of key genes controlling the hepatic GH-IGF axis during the gestation/lactation cycle.
Materials and Methods
A total of 11 cows with good genetic merit for fertility (Fert+) and 12 cows with poor genetic merit for fertility (Fert-) were managed as a single herd under a grass-based system of production. Cows underwent liver biopsy by percutaneous punch technique on d 20 (± 6.7 d) prepartum and on d 2 (± 1.5 d), d 58 (± 3.7 d), d 145 (± 13 d) and d 245 (± 17.1 d) postpartum. Total RNA was isolated and the mRNA expression of growth hormone receptor (GHR 1A and GHRtot), IGF-I, janus tyrosine kinase 2 (JAK2), signal transducer and activator of transcription 5B (STAT5B), suppressor of cytokine signalling 3 (SOCS-3), acid-labile subunit (ALS), and IGF binding proteins (IGFBP1 to IGFBP6) were measured by RT-qPCR. Blood samples were collected coinciding with each biopsy, and circulating concentrations of IGF-I and insulin determined. All data were checked for normality, and transformed if necessary. Mixed models repeated measures analysis were used to compare plasma IGF-I and gene expression data between genotypes. The model included the fixed effects of genotype, time, parity, and their interactions. Cow nested within genotype was included as a random effect. Pre-planned contrasts using the ESTIMATE statement were carried out to compare gene expression data between Fert+ and Fert- cows during three distinct time periods; the dry period (wk -3), early lactation (wk 1 and wk 8), and mid/late lactation (wk 20 and wk 35).
Results and Discussion
During lactation, circulating concentrations of IGF-I were 34% greater in Fert+ cows (P < 0.01). Fert+ cows had increased mean expression of IGF-I mRNA during the study; however, the differences in IGF-I mRNA abundance between Fert+ and Fert- cows was most pronounced at d 145 and d 245. The expression of IGFBP3 and ALS transcripts were similar in Fert+ and Fert- cows for the duration of the study. Fert- cows, however, had greater (P < 0.05) expression of IGFBP2, IGFBP4, IGFBP5 and IGFBP6. There was no effect of genotype on mRNA abundance of GHR 1A, STAT5B, JAK2, or SOCS-3 (P > 0.05).
These results demonstrate that genetic merit for fertility traits affects hepatic expression of key genes of the somatotropic axis regulating the synthesis, bioavailability and stability of circulating IGF-I.
Lucy, M.C. (2001) J. Dairy Sci., 84:1277-1293.
S.B. Cummins, P. Lonergan, A.C.O. Evans and S.T. Butler (2011). Proceedings of the 2011 ARF, page 160.